1. Field of the Invention
The invention relates to a device for detaching sheet material from the surfaces of rollers, which comprises a number of pivotable detaching fingers having front faces which bear against the surface of the rollers.
2. The Prior Art
In electrostatic copying processes, a latent electrostatic image of the original which is to be copied is formed on the image recording material. The electrostatic charge pattern is developed and made visible by the application of toner. In most cases the developed charge pattern is transferred to an image carrier, for example, a sheet of paper, and fixed thereon by the application of heat. In copying machines, driven pairs of rollers attend to the delivery of the image carrier, the application of toner, and the heating of the developed charge image on the image carrier. It is then generally necessary for the image carrier, which, for example, passes out through a gap between two rollers facing one another, to be reliably detached from the roller surface with the aid of a stripping device provided with stripping bars or stripping fingers, in order to ensure rectilinear further delivery of the image carrier or to divert the image carrier from the gap on a prescribed path to a conveyor device, such as a conveyor belt or the like, which delivers the image carrier to the outlet point of the copying machine. A stripping device of this kind is generally in contact with the roller or cylinder surface which--particularly in the case of the image recording drum, which for example is provided with an organic photoconductor or coated with selenium or other photosensitive material--is very susceptible to mechanical influences and can very easily be damaged and functionally impaired thereby.
In German Offenlegungsschrift No. 24 44 876, a stripping device is described as having pivotably-mounted stripping fingers which bear with their leading edges against the peripheral surface of a heated roller. The stripping fingers are pivotable about the free ends of pivot pins anchored at one end in vertical supports which in turn are carried by long rods fastened to a supporting frame of the copying machine. Each stripping finger is provided with a narrow contact edge formed by the line of intersection of a horizontal upper face and of a lower face extending obliquely thereto. This contact edge in the form of a wedge-shaped knife edge is rectilinear and lies against the peripheral surface of the roller. It is obvious that, on the rotation of the roller, this contact edge continuously abrades the surface of the roller within the area of contact and leads to rapid wear of that surface. With this known device, it cannot be ensured that the contact surface of the stripping fingers will lie exactly parallel against the surface of the roller, if there are even slight tolerance deviations of the individual dimensions of the stripping fingers. Instead of the desired linear contact along the contact surface of the stripping fingers, practically only point contact will be achieved, and this will considerably accelerate the wear on the roller surface.
Premature wear of the roller surface must also be avoided for fixing rollers, which generally have a coating of polytetrafluoroethylene of a thickness of up to about 50 .mu.m on the surface.